We have continued our studies of cerebrospinal fluid (CSF) levels of various hormones, peptides, monoamines and monoamine metabolites in rhesus monkeys and man. An investigation of CSF serotonin and melatonin concentrations sampled over 24-hour periods revealed a 20-fold diurnal variation in serotonin in rhesus monkeys. Serotonin concentrations peaked at midnight, and followed a similar time patterns as that for CSE melatonin. Both rhythms were essentially obliterated by continuous light and by the Beta-adrenergic antagonist, propanolol, indicating similar regulatory mechanisms for both substances. Studies with prolactin have demonstrated a blood-CSF gradient for this hormone. In addition, a ventricular-lumbar gradient within the CSF is not present under baseline conditions but develops following prolactin release elicited by treatment with thyrotropin stimulating hormone. Prolactin release elicited by the cholinergic agent, physostigmine, may be modulated by hypothalamic Beta-endorphin release. Studies with the new benzodiazepine receptor antagonist, Beta-carboline ethyl ester in rhesus monkeys have suggested a new pharmacologic model of "anxiety" and provided an opportunity to study the neuroendocrine and catecholamine changes that accompany clinically-relevant behavior in primates.